Motor vehicles are increasingly being equipped with aids which are designed to correct and/or prevent incorrect driving behavior on the part of the person operating the vehicle. For example, one of the measures currently available prevents locking of braked wheels. Other measures consist in providing assistance whenever a vehicle threatens to run off track as a result of a curve being taken too tightly. In order that correction moments which keep the vehicle on track can be applied in conjunction with this so-called yawing moment control system, it is important that the control system be informed of the radius within which the driver intends to operate the vehicle. This is achieved with the help of a steering angle sensor. It should also be noted that the wheel angle is not yet known when the system is switched on, i.e., when power is supplied to the system by turning the ignition key. Consequently, the actual angle of the wheels cannot be obtained by simply adding or subtracting relevant incremental angle changes. Instead, continuous absolute readings must be taken to provide the control system with precise information on the actual angle of the wheels.
It is known that the aforementioned incremental steering angle sensors, which routinely consist of two sensors, cannot provide an absolute steering angle on their own. An additional third sensor (zero point sensor) is needed to provide an absolute steering angle once the circular scanning track has completed a 360 degree rotational movement. This results from the inclusion of a marking on this absolute track which defines the zero point and which is used to calculate the measured absolute reading.
The reference signal obtained in this manner is not confirmed until an additional 360 degree rotation has been completed. Even in the event that the angle of rotation of the steering wheel is very much larger than the angle of rotation of the applicable wheel, the described procedure for obtaining an absolute wheel angle reading is not sufficient for some applications in the vehicle.
The object of the invention is to design a steering angle sensor in such a way that an absolute steering angle value can be determined with simple means and after a relatively small rotational movement.